It is only logical that the materials you select affect the performance of your product. It is the same with printed circuit boards, and choosing the right PCB substrate materials can largely affect performance, durability, and other features of your board.
In this article, we are investigating material requirements in different categories. We will not stop there because we will also focus on how to choose the right materials for your PCB needs and a reliable manufacturer. So, make sure to keep reading to boost your printed circuit board knowledge!
1、Copper Foil Requirements
Image 1: PCB board plated with copper
PCB substrate materials play an integral role in determining the durability and quality of your board. It is noticeable that the manufacturers are trying to move towards fine lines and high density.
You may have heard of the term HDI PCB. It stands for High-Density Interconnect Printed Circuit Board. Approximately ten years ago, a board needed to have line space (S) and line width (L) of not more than 0.1mm to be classified in the HDI category.
Today, the standards vary from one industry to another. Electronic products often have S and L set as low as 60μm, and they can even go to 40μm in advanced applications.
During the process of circuit pattern formation, S and L can reach a value as low as 30μm once you apply a thin substrate made of copper foil. The recommended thickness can go from 9μm to 12μm.
The problem is that CCL (copper clad laminate) that is so thin can be expensive and prone to defects. It is the best explanation for why companies resort to using 18μm-thick copper foil. However, if S and L are not more than 20μm, the copper foil of standard thickness might not be the best solution.
1.1. How Surface Roughness Can Affect the Quality of Your PCB
If your goal is to design a fine circuit, you also need to consider how rough the copper foil surface will be. Roughing will ensure that the conductors have peel strength, as well as that bonding of the substrate material and the copper foil is optimal. The standard roughness nowadays is set to around 5μm.
If you want to boost peel strength, it may be wise to embed hump on the foil into the substrate. In this case, you want to keep the roughness as low as possible (preferably up to 1.5μm, but no more than 3μm).
You may be wondering how to peel strength will be kept if you reduce the foil roughness. The answer lies in the special finish you apply to the surface of both the substrate and the foil. That way, the conductors can maintain optimal peel strength and ensure the reliable performance of your PCB.
2、Insulating Dielectric Laminates
The building up process is an essential property of HDI printed circuit boards. If you use resin-coated copper (RCC) or combine copper foil lamination with the prepreg cloth of epoxy glass, there is a good chance you will design a fine circuit.
The manufacturers have also implemented the MSPA and SAP technologies. That secured generation of the copper conducting plane by applying insulating dielectric film lamination with chemical copper playing. It is the thin copper plane that is the main reason why we can produce fine circuits.
2.1. Why Lamination Dielectric Material Is Crucial for SAP
We need to consider lamination material and its requirements if we are going to design HDI PCBs. Some considerations include dielectric performance, thermal capacity, insulation, and bonding.
If you take a look at packages with semiconductivity, the IC package may turn organic substrate from the ceramic. A decrease in the size of the FC package is noticeable as the values of S and L are around 15μm with the tendency to become even more compact.
Multi-layered PCB substrate materials should help to reduce the thermal expansion coefficient and dielectric property while securing optimal resistance to heat. This type of substrate is a good choice as it can achieve all performance goals while maintaining an acceptable cost.
We use SAP technology in the manufacturing process of circuits when their space and width are below 10μm. In fine circuit production on a large scale, MSPA can be applied to use thin copper foil to insulate dielectric lamination.
Image 2: A yellow printed circuit board from the backside
3、Why High Speed and High Frequency Are Important for Your PCB
Technology is making huge progress every day. We have seen innovations like using wireless connections, high speeds, and high frequencies.
Smartphones are already taking advantage of the 5G network, which has impressive data speed and bandwidth capabilities. The high-speed design has been the topic of many experts in the industry.
The data traffic boost means we need to design devices that can handle those high speeds and frequency. It is why it is essential to use materials that can deliver extraordinary performance while keeping the integrity of the signal and minimizing interference.
We can make a difference between:
• Medium Dk/Df laminate PCBs – these have Df no higher than 0.010, and Dk of maximum 4.
• Low Dk/Df laminate PCBs – in these boards, Df is less than 0.005 while Dk is no more than 3.7.
Image 3: Person working on installing PCB on a smartphone
3.1. What Can Types of Substrate Materials Be Used in High-Frequency PCBs?
You can find suitable material in one of the following:
• Fluorine-series resin – materials like PTFE have excellent dielectric performance and can be a great choice if you need at least 5GHz
frequency. Their cost is probably the highest of all three types, and they have a high thermal expansion coefficient. However, they perform impressively in areas of dielectric loss and constant and absorbing water.
• PPO or PPE resin – a suitable option for 1-10GHz frequencies. They secure an all-around decent performance of your board.
• Modified epoxy resin – they can also be a good choice for frequencies between 1GHz and 10GHz. In general, they have the most affordable cost, which is the reason for their popularity.
For example, we will consider PTFE, which falls into the fluorine-series category. It has excellent dielectric performance and can be a great choice if you need at least a 5GHz frequency.
Please note that signal loss may also be due to the high roughness of the copper. It is why you should ensure to keep copper roughness under 1μm. Furthermore, it may be wise to go with roughness no bigger than 0.04μm.
4、Thermal Requirements of PCBs
If you want to pack impressive performance in a compact size, it is only normal that the device produces a lot of heat. That is why an important consideration must be how to meet these requirements in managing that heat.
The goal should be to create thermal-conducting boards of reliable and extraordinary performance. You should carefully consider PCB substrate materials as they are the key to handling heat dissipation and resistance.
Today, we can see improved resins and added the filling, but that is not a recipe that always works. You can consider applying IMS or metal core boards to act as heating components. Thanks to this, you may achieve a more acceptable cost and smaller size compared to using a fan or radiator.
1.1. What Would Material Be the Best Choice for Heat Conductivity?
If we are talking about combining excellent heat conductivity, availability, and optimal cost, it seems that the material of choice should be aluminum.
It is not only about the price because aluminum can secure a stable electric connection while keeping everything lead and solder-free. It's no wonder that we can see aluminum PCBs in automotive, aerospace, and military industries, as well as consumer electronics.
Image 4: Printed circuit board PCB burning
5、How to Choose PCB Substrate Materials
You have the choice of picking from three different PCB types:
The primary goal is to pick a board that will be perfect for your product. Many people aim for compact size and shape, but they forget about performance.
Polyimide film can be a smart choice as it is versatile, and it can fit into different categories like black, white, and transparent. It also ensures a low thermal expansion coefficient while maintaining adequate resistance to heat.
Mylar substrate, on the other hand, is very elastic, and it has excellent resistance to environmental factors. On top of that, it is relatively affordable, which is why many users consider it.
Flexible PCBs have to strive to achieve the same level of performance in terms of frequency and speed as standard PCBs. Advanced polyimide substrate and polytetrafluoroethylene are smart choices for flexible boards.
You can find flexible boards in many industries, including medicine, smartphone, and the gadget industry. That is why the market has been implementing changes in the form of multi-layer boards that are flexible and extra thin (0.2-0.4mm).
At this point, you can expect flexible boards to secure speed of up to 5Gbps, but you will need to use a low Dk/Df substrate material. It is also smart to use conductors that have over 100μm of thickness as that will help to handle the amounts of current and power.
Image 5: A close up look at the printed circuit board
6、Where to Manufacture PCBs?
Image 6: PCB factory close up – manufacturing printed circuit boards
Once you have all the materials selected, OurPCB is an excellent choice for manufacturing and assembly. It is a company that has over a decade of tradition, and more than 2,500 customers throughout the world at the moment.
The company employs experienced and skilled engineers and uses exceptional equipment to meet client’s requests.
Here are some advantages of OurPCB:
• Choose the desired board type – it doesn’t matter if you need rigid of flexible PCB because the company can cater both.
• Customize your order – choose details like the number of layers, copper and board thickness, etc.
• Simple ordering process – you can contact the company with your demands, and they will secure a quote within eight working hours. The PCBs delivered to the entire world via FedEx, DHL, EMS, and TNT.
PCB substrate materials play a crucial role in the quality and performance of any printed circuit boards. That is why it is crucial to know more about the topic, and that is what this article provided.
Aside from choosing the right materials, you also need to pick a reliable company that can manufacture your desired board. OurPCB is a great choice if you are looking for the best combination of affordable price and high quality.